A double-wheel trench cutter is a foundation engineering construction machine with high construction efficiency. In the double-wheel trench cutter, a hydraulic motor drives a decelerator to drive a cutting wheel to cut rocks into trench, with the maximum cutting depth reaching 150 m. With the increase of the cutting depth, the pressure of a motor oil drainage cavity also increases. The oil drainage cavity of the common motor adopts a lip seal, and the maximum pressure borne by the common motor is 0.3 MPa, so the common motor at the depth of more than 30 m cannot meet the pressure bearing requirement and thereby cannot work normally.
In order to solve the pressure bearing problem of the motor, in the prior art, a specially designed motor is adopted, see FIG. 1, specifically, the lip seal of the motor oil drainage cavity is changed into a mechanical seal, and the mechanical seal is at the same position as the lip seal and is between a motor shell and a motor output shaft.
The inventor discovers that, the prior art has the following problems: in the prior art, although the mode of changing the lip seal of the motor oil drainage cavity into the mechanical seal can solve the pressure bearing problem of the motor, the special design of the motor may lead to difficulty in purchase and maintenance of the motor, meanwhile, the purchase cost of the motor may be greatly increased, so that it is unfavorable for the popularization of the double-wheel trench cutter.